Survey for Distant Solar Twins (SDST) -- III. Identification of new solar twin and solar analogue stars

TL;DR

This survey identifies new distant solar twins and analogues using a differential spectroscopic technique, enabling the selection of prime targets for testing fundamental physics variations across the Galaxy.

Contribution

The paper introduces EPIC, a line-by-line differential method for stellar parameter measurement, applied to distant stars, expanding the catalog of solar twins and analogues at 1-4 kpc.

Findings

Identified 299 new solar analogues with high confidence.

Discovered 20 solar twins at 1-4 kpc with precise stellar parameters.

Selected 174 inactive, slowly rotating solar analogues suitable for further study.

Abstract

The Survey for Distant Solar Twins (SDST) aims to find stars very similar to the Sun at distances 1-4 kpc, several times more distant than any currently known solar twins and analogues. The goal is to identify the best stars with which to test whether the fine-structure constant, alpha, varies with dark matter density in our Galaxy. Here we use EPIC, our line-by-line differential technique, to measure the stellar parameters - effective temperature Teff, surface gravity log g, metallicity [Fe/H] - from moderate resolution (R < 32,000) spectra of 877 solar twin and analogue candidates (547 at 1-4 kpc) observed with the HERMES spectrograph on the Anglo-Australian Telescope. These are consistent with expectations for Teff and log g from photometry, and for [Fe/H] from the Besancon stellar population model. EPIC provides small enough uncertainties (~90 K, 0.08 dex, 0.05 dex, respectively), even at the low signal-to-noise ratios available (S/N >~ 25 per pixel), to identify 299 new solar analogues (> 90% confidence), and 20 solar twins (>50% confidence), 206 and 12 of which are at 1-4 kpc. By extending EPIC to measure line broadening and lithium abundance from HERMES spectra, and with ages derived from isochrone fitting with our stellar parameters, we identify 174 solar analogues at 1-4 kpc which are relatively inactive, slowly rotating, and with no evidence of spectroscopic binarity. These are the preferred targets for follow-up spectroscopy to measure alpha.